Process for the production of low carbon metals and alloys



Patented Apr. 2, i940 2,195,961

UNITED STATES PATENT OFFICE PROCESS FOR THE PRODUCTION OF LOW CARBON METALS AND ALLOYS Ture Robert Haglund, Stockholm, Sweden No Drawing. Application September 20, 1937, Serial No. 184,815. In Sweden September 29, 1936 23 Claims. (Cl. 75-89) The present invention relates to the production the form of fine particles. The temperature and of low carbon metals and alloys by means of the the composition of the reacting materials are suitreductlon of one or several oxides, or material ably adjusted so that the reduction of the oxide of containing oxides, of elements with the atomic the metal by means of silicon contained in the numbers 23-28, viz. vanadium, chromium, iron, alloy will be entirely or at least chiefly brought 5 manganese, cobalt, and nickel, using silicon metal about Wi out any x e a heat pp y- The Silior a silicon alloy as a reducing agent, con alloy is thus also preferably introduced in a By earlier known processes of this kind, the m e State, bu ay, if d d, be charged in procedure has been to employ an electric furnace a Solid S a e. e- 8- in e form of lumps of p w e 10 provided with one or several electrodes, in which In th la t r 0359,33! sp y w n it is d sired a mixture of the oxide containing material and to reduce n oxide n he slag avin a p r icua silicon alloy have been fused, thus e. g. in the lerly high t of o a 8- chromium case of the production of ferro-chrome, chromium Oxide. 1t however, Suitable either to D e-h a ore together with li a sum h or ferro the silicon alloy outside the reaction furnace or silicon having a high content of silicon. Other else to D t 0 e t e Sa e n the urnace silicon alloys such as silicon-calcium and siliconbefore introducing the molten 8- Y dj t aluminium alloys have also been employed in such the Composition of the Oxide 1 8, as Well as its processes for the production of ferro-chrome. In temperature. it 18 so P ible to store the mosscertain cases the silicon alloy, instead of being heat in this for y g out the p s- 20 fixed with the unfused charge, has been intro- When Produeins t rm-chrome by means or the duced in a molten state. A disadvantage when P It 18 thus advisable to e t a S ag with using these processes has been that the resulting high cement of chromium Oxide having a comalloy, owing to the protracted fusing time, has a paratively high meltmfl P and to p e tendency to absorb carbon from the electrodes. temperature of the B 88 during the charging into 95 A th r dlsadvantage t t t t must be the reaction furnace at least 100 C. and preferstrongly superheated in order to obtain equiably more e 0 0- higher than the temperau m b t the slag t and t alloy ture of solidification of the ferro-chrome.

order to overcome this latter disadvantage it has The reaction furnace 18 P e ab y built as a een suggested to intimately mix slag and metal rotary furnace in the form of a cylinder with its in connection with the tapping of the furnace, axis of revolution Winch-11118 With the a s 0 he 80 e. g. by letting the metal from a high level strike cylinder and being mounted o tally or a slag bath in such a manner that the metal will slightly incllned t0 the horizeiltel- A rotating become intermixed in a finely divided state with speed of from 1 to 5 utions per minute is t SM This tt procedure W111, however generally quite suilicient. If it is particularly cause conslderame losses owing to the fact that desired to accelerate the reaction velocity, the the particles of metal will not have sufllcient time speed of rotation may be increased. e- 8. up to to completely separate from the slag and the 10 R. P. M. 01 more. It 15 8.150 possible for this is also the danger that the metal, because of the purpose to employ furnace container p ovided violent stirring, will come in contact with great with a stirring device, e. g. built of or coated with quantities of air, from which it may absorb nitrorefractory material. A rotary u nace is, howgem 1 these dgsadvantages are eliminated when ever, as a rule to be preferred. The molten metalusing the process according to the present invenbath is by means of the rotation ought into om circulation so that fresh parts of the metallic According to the present invention, l carbon bath will be conveyed to the contact zone between 45 metals or alloys are produced by means of intrometa-111 bath and Slag bath- T e slag is also ducmg 11m t or i i alloy, and brought into motion by the contact with the cirmolten slag containing one or several oxid of culating metallic bath as well as with the furnace the metals vanadium, chromium, manganese, wall. This will cause a removal from the contact iron, cobalt or nickel, in a reaction furnace or zone between metallic bath and slag of such, slag 50 container, and imparting to the charge a comextremely rich in silica, which would otherwise paratively slow movement to accelerate the rehave a strongly retarding influence on the reaction; 1. e. the movement should not be so strong action between metallic bath and slag. This slag that it causes the metallic bath to become disinis instead in this manner replaced by a slag richer I tegrated and intermixed with the slag bath in in oxides. By increasing the number of revoluas tions of the rotary furnace, the movement of the metallic bath and the slag will also be increased, making it possible to cary out the reaction in a very short time whereby heat-losses due to radiation are considerably reduced. In addi- .tion to an almost immediate removal of the slagfilm rich in silica as soon as this forms, amovement is also imparted to any crystal particles which may be formed and which are heavier than the rest of the slag and thus otherwise would tend to form a slurry immediately above the surface of the metallic bath. Such formation of crystals which i. e. often occurs in the form of chromiumspinel crystals in slags rich in chromium oxide, will often render the obtaining of an equilibrium between metallic bath and slag impossible in the known refining processes. By introducing the silicon alloy in a molten state and only adding the fluid slag after this has been made, the advantage is obtained-that the metallic particles produced by the reduction will separate out at the surface of the metallic bath and immediately become absorbed in this; This makes it possible to avoid such sometimes rath'er heavy losses of metal which, in cases when the reduction takes place within the slag bath, will ensue because of the fact that the finely dispersed metallic particles in the slag, will not have suflicient time to settle. Also in such cases, when the starting material according to the present process consists of a pulverized silicon alloy, there is always the advantage that the metallic particles dispersed in the slag, by the slow movement of this latter, will more easily be brought into contact with and become absorbed by the metallic bath. This movement of the slag bath is of a particularly great importance for the separation of metallic particles from the slag in such cases when this latter has a tendency to form a precipitate of crystal-slurry on top of the metallic bath.

The slag which holds the oxide is produced in a separate furnace, preferably of the tilting type, and tapped into the rotary furnace, either in one or several portions or in such a manner, e. g. by regulating the tilting of the furnace in which the slag is produced, that it will be poured into the rotary furnace more or less continuously for a certain period of time. In the latter case it is suitable to let the slag flow over the metallic bath in a comparatively thin layer from one end of the rotary furnace,-at the same time letting the reduced slag chiefly escape from the other end of the furnace. The first portion of the outfiowing slag, which has reacted with an alloy richer in silicon than that part of the slag which is leaving the furnace at the end of the reaction period,-.wili

thus be in a more completely'reduced state than I The slag which is tapped from the;

this latter. I rotary furnace during the latter part of the reaction, thus having a composition more resembling that of the fresh slag, is suitably recovered separately for a utilizing of its oxide content. A similar dividing of slag into one more completely reduced portion and one or several portions of less completely reduced slag, may also be effected by means of charging and tappingthe oxide slag in the rotary furnace in two or several portions. When producing ferro-chromium according to the present process, it is thus suitable to produce a slag rich in chromium oxide having a chromium oxide content of e. g. from to 60 per cent, in a separate electric furnace, from chromium ore and lime preferably also using a certain amount of a reducing agent. If the reduction in the rotary furnace is accomplished by means of a ferrosilicon alloy, it is suitable to remove the whole or part of the iron oxide in the chromium ore by means of reduction in combination with the production of the slag. This is done for the purpose of beingable to obtain a high content of chromium in the ferro-chromium, in spite of the iron contained in the ferro-silicon. If, on the other hand, a silico-chromium alloy having a comparatively low content of iron is used, a separation of iron oxide from the chromium ore is of less importance. After fusing a sumcient quantity of slag, which is suitably also superheated, a quantity of fused ferro-silicon, preferably with a silicon content between 60 and 80 per cent, or else a silico-chromium alloy, e. g. having a silicon content of about 30 to 50 per cent Si, is tapped into the rotary furnace, after which the fused slag rich in chromium oxide is added. The slag may also be added previous to the silicon alloy or else both be added simultaneously. The addition of slag is suitably divided in such a manner, that a smaller portion than what may be reduced by means of the silicon in the alloy is first tapped into the rotary furnace. The furnace is put into rotation and as soon as the reaction commences to stop the whole or main pazt of the slag formed by the reduction is tapped ou After this, a new quantity of slag rich in chromium oxide is one or several times added while working the furnace in aforementioned manner. By dividing the adding of the slag rich in chromium oxide into several stages or charges, the advantage is obtained, that the content of chromium oxide in those slag portions which are withdrawn while the alloy still contains considerable quantities of silicon may be kept particularly low, from traces up to about 10 per cent. During the last stage of the reduction process the content of chromium oxide is' kept high, preferably between 20 and 30 per cent, or more, by introducing slag in excess of the amount of slag reducible by the silicon content remaining in the alloy. In certain cases it may also be advisable to add a new amount of silicon alloy, after a first reaction between the slag and alloy has been effected in the rotary furnace. By dividing the addition of the slag rich in chromium oxide in the above-mentioned manner, the advantage is obtained that those reaction products which are first formed will have a lower melting point than would otherwise be the case, and that the rotary furnace is heated by the sensible heat of the slag rich in chromium oxide and by the heat of reaction before the formation of the final less fusible reaction products is effected. The reaction slag obtained in the process which is comparatively rich in chromium oxide may either be returned to the slag-producing furnace, e. g. when still in a molten state, or

else be utilized for the production of a silicochrome alloy, or for some other purpose.

The rotary furnace is preferably made of the tilting type so that slag, as well as metal, may be drawn off by tilting the furnace. If the slag is conveyed in a comparatively continuous stream through the furnace during the reaction process, the thickness of the layer of slag may be regulated by a tilting of the furnace. In order to increase the stirring action in the furnace, this may be built with some other section than a circular one, e. g. by being internally provided with longitudinal flanges or projections. Since the process of reaction inthe rotary furnace is very rapid, it will as a rule not be possible to utilize the furnace to full capacity. The furnace should therefore be it will not cool down well heat-insulated so that too much between the periods during which it is used. The furnace should as a rule be preheated before each new reaction period. This may be accomplished by electricity, e. g. by radiation from a resistance or an electric are, or else by gas heating.

The present invention may also be used for the production of alloys having a high content of the metals chromium, manganese and vanadium, as for the production of alloyed iron and steel, e. g. low carbon chrome steel and chromenickel steel. In the foregoing the invention has been described in connection with the production of low carbon ferro-chrome. The production of chrome steel is carried out in a similar manner. Low carbon iron is produced in a special furnace, in which case, if nickel is to form part of the alloy, the nickel should also be supplied to the same furnace. Silicon, e. g. in the form of ferro-silicon with a silicon content of about 50 per cent is supplied to the low carbon iron, preferably also before the iron is poured into the rotary furnace. The silicon is added in an amount necessary for separating out the desired quantity of chromium. The silicon containing iron is then poured into the rotary furnace, whereupon the slag rich in chromium oxide is supplied in the manner described above, in one or more portions, or continuously. when the silicon content, by being utilized as a medium of reduction for the oxides of chromium and iron which form part of the slag, has become reduced to the percentage desired in thefinal alloy, and this latter alloy, if necessary by the supply of additional heat has been given a suitable tapping temperature, the chorme steel, by tilting the rotary furnace, is delivered to a ladle or some furnacein which the desired after-adjustment of the composition of the alloy may be effected. By superheating the low carbon iron, preferably before it is introduced into the rotary furnace, it is possible to a certain degree to compensate for the cooling of the rotary furnace between the periods of use. When producing alloys with a chromium content of about 13 to 30 per cent, a silicon content of 8 to 25 per cent in the iron supplied to the rotary furnace is as a rule sumcient. When the silicon is added to the iron, wholly or in part in the form of an alloy of silico-chrome, such a large quantity of silicon need not be supplied to the iron as when the additions consist entirely of ferro-silicon.

For producing the slag containing chromium oxide, chromium ores with a high or low content of chromium may be used. If the chromium ores contain more oxide of iron than is desirable, part of the iron may preferably be separated of! before the slag is poured into the rotary furnace. It is also possible to remove practically all the iron and at the same time reduce part of the chromium oxide, in which case chrome steel may be obtained as a by-product from the slag-producing furnace. This reduction may be eflected by supplying a carbonaceous reduction material, such as coke or anthracite; it is however also possible to use silicon, wholly or in part, as a medium of reduction. e. g. in the form of ferrosilicon. In view of the fact that the content of chromium oxide should be kept high, preferably not below 15 to 20 per cent, at the final refor reducing chromium oxide in much poorer' slags. If the chromium oxide slag has a considerably higher temperature than the necessary tapping temperature of the final product, a greater amount of slag and thus also of surplus heat will, furthermore, be supplied to the rotary furnace with the chromium oxide slag, the smaller the content of chromium oxide is in the slag.

In the production of low carbon chromium alloys it is of great importance to employ silicon alloys with a low carbon content. For this reason it is often advisable to subject such alloys to a refining process for reducing the carbon content by smelting or mechanical concentration; in the latter case after crushing to such a grain-size that a considerable part of the impurities separated out in the crystal boundaries of the alloy may be removed by wet or dry concentration process.

The production of low carbon alloys of manganese and vanadium is, on the whole, effected in the same manner as that described in connection with the production of chromium alloys. It is generally desirable to keep the percentage of manganese in ferro-manganese alloys as high and the iron content as low as possible. For this reason a silicon alloy such as silico-manganese, is preferred as a reducing agent when low-carbon ferro-manganese is produced according to the invention. When ferro-vanadium is produced it is, on the other hand, as a rule preferred to employ ferro-silicon as a reducing agent. Oxides of iron contained in the manganese ore may, wholly or in part, be separated before the molten slag rich in manganese is supplied to the rotary furnace. should be added when producing the slag of manganese oxide, since otherwise the slag having a high silica content and which is formed in the rotary furnace may easily become too viscous. Slags from the method for the purpose of recovering their content of manganese.

the extraction same at least during part of said period.

2. In the production of low carbon metals and alloys containing at least one metal of the group with a low iron content,

ing of the slag with bath, the heat content and temperature of said slag being sufficiently high to promote the desired reduction reaction without the addition of external heat and during the resulting reaction agitating said bath in such manner as to produce a minimum of intermixing.

3. The process of claim 2 wherein said slag is added in stages to said bath'until sufficient oxide has been reduced to produce the desired composition.

4. In the production of low carbon iron-chromium alloys, the process which comprises establishing a molten bath comprising iron and a sill:

con-containing reducing agent, adding a molten slag containing from about 30 to 60 per cent chromium oxide and of a sufilciently high temperature to promote the resulting reduction reaction without further heating, and during said reaction agitating said bath in such manner as to produce a minimum of intermixing.

5. The process of clair' 4 wherein the said molten slag is added in stages, the slag added in the final stage having such a composition that its content of chromium oxide remains above about per cent during the reduction reaction.

6. The process of claim 4 wherein the said slag is passed substantially continuously over the surface of said molten bath.

'7. In the process of producing low carbon metals and alloys containing at least one element belonging to the group vanadium, chromium, manganese, iron, cobalt and nickel, wherein a molten slag containing at least one oxide of such an element is contacted with a molten metal bath comprising a silicon-containing reducing agent, the steps which comprise introducing a silicon alloy and the fluid slag in a rotatable cylindrical receptacle with a minimum of agitation, and promoting the resulting reduction reaction between the silicon and the slag by slowly rotating said receptacle about its axis in such manner as to produce circulation without substantial intermixsaid molten metal bath.

8. In the process of producing low carbon metals and alloys containingat least one element belonging to the group vanadium, chromium,

manganese, iron, cobalt and nickel, wherein a molten slag containing at least one oxide of such an element is contacted with a molten metal bath comprising a silicon-containing reducing agent, the steps which comprise introducing a silicon alloy and the fluid slag in a cylindrical receptacle with a minimum of agitation, said receptacle being rotatable about a substantially horizontal axis, and promoting the resulting reduction reaction between the silicon and the slag by slowly rotating the said receptacle about its axis in such manner as to produce circulation withoutsubstantial intermixing of the slag with said molten metal bath.

9. In the process of producing low carbon metals and alloys containing at least one element belonging to the group vanadium, chromium, manganese, iron, cobalt and nickel, wherein a molten slag containing at least one oxide of such an element is contacted with a molten metal bath comprising a silicon-containing reducing agent, the steps which comprise introducing a silicon alloy and the fluid slag in a rotatable and tiltable, cylindrical receptacle with a minimum of agitation, promoting the resulting reduction reaction between the silicon and the slag by slowly rotating said receptacle about its axis in such manner as to produce circulation without substantial intermixing of the slag with said molten metal bath and tapping it by means of tilting.

10. In the process of producing low carbon metals and alloys containing at least one element belonging to the group vanadium, chromium, manganese, iron, cobalt and nickel, wherein a molten slag containing at least one oxide of such an element is contacted with a molten metal bath comprising a silicon-containing reducing agent,

- the steps which comprise introducing in a rotatable, cylindrical receptacle with a minimum of agitation, a molten silicon alloy and the fluid slag and promoting the resulting reduction reaction between the silicon and the slag by slowly rotating the said receptacle about its axis in such manner as to produce circulation without substantial intermixing of the slag with said molten metal bath.

11. In the process of producing low carbon metals and alloys containing at least one element belonging to the group vanadium, chromium, manganese, iron, cobalt and nickel, wherein a molten slag containing at least one oxide 0! such an element is contacted with a molten metal bath comprising a silicon-containing reducing agent, the steps which comprise introducing in a rotatable, cylindrical receptacle with a minimum of agitation, a molten silicon alloy and the fluid slag, regulating the temperature and the composition of the added materials so that enough heat is accumulated in these for carrying out the reduction reaction without supplying external heat during the reduction, and promoting the reduction reaction between the silicon and the slag by slowly rotating the said receptacle about its axis in such manner as to produce circulation without substantial intermixing of the slag with said molten metal bath.

12. In the process of producing low carbon metals and alloys containing at least one element belonging to the group vanadium, chromium, manganese, iron, cobalt and nickel, wherein a molten slag containing at least one oxide of such an element is contacted with a molten metal bath comprising a silicon-containing reducing agent, the steps which comprise introducing in a rotatable, cylindrical receptacle with a minimum of agitation, a silicon alloy and part of the fluid slag, which is to be reduced by the silicon, slowly rotating the receptacle about its axis in such manner as to produce circulation without substantial intermixing of the slag with said molten metal bath, thereafter tapping out the treated slag and introducing a further portion of the fluid slag to be reduced.

13. In the process of producing low carbon metals and alloys containing at least one element belonging to the group vanadium, chromium, manganese, iron, cobalt and nickel, wherein a molten slag containing at least one oxide of such an element is contacted with a molten metal bath comprising a silicon-containing reducing agent, the steps which comprise introducing in a rotatable, cylindrical receptacle with a minimum of agitation, a preheated solid silicon alloy and the fluid slag, and promoting the resulting reduction reaction between the silicon and the slag by slowly rotating the said receptacle about its axis in such manner as to produce circulation without substantial intermixing of the slag with said molten metal bath.

14. In the process of producing low carbon.

metals and alloys containing at least one element belonging to the group vanadium, chromium, manganese, iron, cobalt and nickel, wherein a molten slag containing at least one oxide of such an element is contacted with a molten metal bath comprising a silicon-containing reducing agent, the steps which comprise introducing a solid silicon alloy in a rotatable, cylindrical receptacle with a minimum of agitation, heating said alloy in the receptacle and thereafter introducing the fluid slag, and promoting the resulting reduction reaction between silicon and slag by slowly rotating the receptacle about its axis in such manner as to produce circulation without substantial intermixing of the slag with said molten metal bath.

15. A process for producing a chromium alloy of low carbon content comprising forming in a separate furnace a slag containing chromium oxide in excess of 30 per cent, introducing in a rotatable, cylindrical receptacle with a minimum of agitation, a silicon alloy and a fluid portion of said chromium oxide slag, slowly rotating the receptacle about its axis in such manner as to produce circulation without substantial intermixing of the slag with said molten metal bath and regulating the relative amounts of silicon and chromium oxide so that a slag containing less than 10 per cent of chromium oxide results, thereafter tapping ofi and introducing a further portion of the fluid chromium oxide slag, and regulating the latter amount in relation to the amount of silicon still contained in the metal bath, so that the slag resulting from the continued reaction will contain at least 15 per cent chromium oxide.

16. In the process of producing alloys of low carbon content containing iron and at least one other metal belonging to the group vanadium, chromium, manganese, cobalt and nickel, wherein a molten slag containing the oxide of such other metal is contacted with a molten metal bath comprising a silicon-containing reducing agent, the steps which comprise introducing in a rotatable, cylindrical receptacle with a minimum of agitation, iron and a silicon alloy, heating and thereafter introducing the fluid slag, and promoting the resulting reduction reaction between the silicon and the slag by slowly rotating the said receptacle about its axis in such manner as to produce circulation without substantial intermixing of the slag with said molten metal bath.

17. In the process of producing alloys of low carbon content containing iron and at least one other metal belonging to the group vandium, chromium, manganese, cobalt and nickel, wherein a molten slag containing the oxide oi such other metal is contacted with a molten metal bath comprising a silicon-containing reducing agent, the steps which comprise introducing in a rotatable, cylindrical receptacle with a minimum oi agitation, molten iron, a molten silicon alloy, and the fluid slag, and promoting the resulting reduction reaction between the silicon and the slag by slowly rotating the said receptacle about its axis in such manner as to produce circulation without substantial intermixing oi the slag with said molten metal bath.

18. In the process of producing alloys of low carbon content containing iron and at least one other metal belonging to the group vanadium, chromium, manganese, cobalt and nickel, wherein a molten slag containing the oxide of such other metal is contacted with a molten metal bath comprising a silicon-containing reducing agent, the steps which comprise introducing a molten iron alloy containing silicon and the fluid slag into a rotatable, cylindrical receptacle with a minimum of agitation and promoting the resulting reduction reaction between the silicon and the slag by slowly rotating the said receptacle about its axis in such manner as to produce circulation without substantial intermixing of the slag with said molten metal bath.

19. A process for producing chromiumalloyed iron and steel, comprising introducing a molten iron bath into a rotatable, cylindrical receptacle with a minimum of agitation, dissolving a silicon alloy in said bath, and thereupon introducing a chromium oxide-containing slag into the receptacle with a minimum amount of agitation and promoting the resulting reduction reaction between the silicon and the slag by slowly rotating the said receptacle about its axis in such manner as to produce circulation Without substantial intermixing of the slag with said molten metal bath.

20. A process for producing chromium alloyed iron and steel comprising forming a bath. of molten iron alloy containing 8-25 per cent silicon in a rotatable, cylindrical receptacle, introducing a fluid chromium oxide-containing slag in the receptacle with a minimum of agitation, and promoting the resulting reduction reaction between the. silicon and the slag by slowly rotating the said receptacle about its axis in such manner as to produce circulation without substantial intermixing of the slag with said molten metal bath.

21. A process for producing chromium alloyed iron and steel, comprising introducing a molten iron bath into a rotatable, cylindrical receptacle, dissolving a silico-chromium alloy in the iron bath and thereafter introducing a fluid chromium oxide-containing slag with a minimum of agitation, and promoting the resulting reduction reaction between the silicon and the slag by slowly rotating the said receptacle about its axis in such manner as to produce circulation without substantial intermixing of the slag with said molten metal bath.

22. A process for producing stainless iron and steel, comprising introducing in a molten condition into a rotatable, cylindrical receptacle with a minimum of agitation, nickel alloyed iron, ferro-silicon, and a chromium oxide containing slag, and promoting the resulting reduction reaction between the silicon and the slag by slowly rotating the said receptacle about its axis in such manner as to produce circulation without substantial intermixing of the slag with said molten metal bath.

23. A process for producing chromium alloyed iron and steel, comprising introducing into a rotatable, cylindrical receptacle with a minimum of agitation, in a molten condition iron, ferrosilicon, and a chromium oxide containing slag, and promoting the resulting reduction reaction between the silicon and the slag by slowly rotating the said receptacle about its axis in such manner as to produce circulation without sub stantial intermixing oi the slag with said molten metal bath.

TURE ROBERT HAGLUND. 

